Enzyme Activities Related to Cyanophycin Metabolism in Heterocysts and Vegetative Cells of Anabaena spp.

The cyanophycin granule polypeptide (CGP) is known to serve as a nitrogen reserve protein in cyanobacteria and is mobilized during nitrogen starvation. An exopeptidase, provisionally called cyanophycinase, which degraded CGP in vitro has been studied, and its product characterized, in two N2-fixing Anabaena species. The enzyme had a pH optimum of 8·5, had no requirement for monovalent or divalent cations and was inhibited by l-arginine and l-aspartic acid. The product of this enzyme was an aspartic acid-arginine dipeptide. A higher activity of both arg-poly(asp) synthetase and cyanophycinase was observed in extracts of heterocysts of both Anabaena species than in vegetative cells. This supports the view that CGP has a dynamic role in nitrogen metabolism of cyanobacteria as well as a storage function.